However, Ring tends to not put as much emphasis on the fullness of the bite (from what I've been told from Ring decoys), whereas in PSA you get judged on how full the grip is.
I'm glad to see this discussion here. Although I don't always have the time to read all the posts and write answers, I always manage to do some "rounds"!
I'd like to comment on the above quote. In French Ring the Decoys at level 2 & 3 have the green light to use ALL of their moves on the dogs. One of the main objectives is to try not to get bit by the dog and once bitten try to get him off the bite (within the rules of course). So we're constantly looking for any loopholes or gaps in the training and/or the dogs' temperament.
With this in mind, it'll be almost impossible for a dog in those levels to get a full mouth grip on a good, agile and competent decoy. Judging depth and quality of grip in this sport would be unfair. On the other hand they do
judge tenacity of the dogs' character and training for staying
on the bite. If the dog changes his grip or lets go of the decoy, major points are lost.
"Trainingwise", all good Ring trainers train their dogs for a full bite. They'll teach the traditional "spots" like front and back legs, flee's, upper body bites, etc. Not always getting a dog to perform them in trials is irrelevant as long as he stays on the bite.